Grain Shape Dependent Thermal Conductivity of Polycrystalline Nanostructure

We employed phonon transport simulations to provide insights into the relation between the grain shape of polycrystalline nanostructures and their thermal conductivity. Two types of polycrystalline nanostructures were modeled by using space-filling structures: one comprised of only a single grain shape (body-centered cubic, face-centered cubic, and simple cubic), and the other featuring two grains of differing sizes constructed by truncating vertices of cubes and filling the resulting volume. For the latter structures, various polycrystalline structures were created by tuning the truncation volume. Our phonon transport simulations in polycrystalline structures consisting of only single shape grains revealed that the boundary-scattering phonon mean free path, which determines the thermal conductivity of nanostructured materials, can vary by up to 10% depending on the grain shape. In addition, the mean free path increases with greater disparities in grain size in the polycrystalline nanostructures, with variations reaching up to about 10%. Furthermore, we found that the mean free path derived from phonon transport simulations is quantitatively consistent with the grain volume-to-surface area ratio in modeled polycrystalline nanostructures. This consistency indicates that the mean free path in polycrystalline nanostructures can be predicted using descriptors based on their fundamental structural features, without the need for numerical simulations.